In both radio and landline telephone systems, a user typically communicates by means of a handset that includes a speaker at one end which is placed close to the user's ear and a microphone at the other end which is held close to the user's mouth. Thus, the user has only one free hand since the other must be used to hold the telephone handset. In order to provide a greater degree of freedom to the user, speakerphones have been developed for use in telephone systems.
A conventional speakerphone, when enabled, allows hands-free use of the telephone while still communicating with another party. However, when a speakerphone is used in a phone conversation there often heard a large disparity in volume between users who are talking close to the speakerphone and those that are distant from the speakerphone. In addition, there are often differences between different user voice levels, which can compound the disparity in volume. Moreover, when a speakerphone function is designed into portable electronic devices, such as radiotelephones, the disparity in user voice levels through the speakerphone is further compounded due to the power limitations of this type of device.
An important problem in the design of portable audio appliances, such as radiotelephones, is that of dealing with acoustic limitations and power limitations of the audio subsystem. This is inherent in the limited size of the acoustic devices used and the power limitations of the audio circuits, particularly in view of the limited power available from a battery. As a result, too much gain in the audio circuits will cause distortion in a device due to either power limitations or acoustic limitations.
Accordingly, there is a need for an improved audio system in a communications device. In particular, it would be of benefit to provide improved audio quality such that low level voices or sounds could be heard as well as high level voices or sounds. It would also be advantageous if such improvement could be provided in a flexible and low cost implementation.